1. Field of the Invention
The present invention relates to an aqueous ink for an inkjet.
2. Description of the Related Art
An inkjet recording system is a printing system in which printing is conducted by spraying a liquid with a high degree of fluidity from very fine nozzles and onto a recording medium such as a sheet of paper. These systems enable the printing of high-resolution, high-quality images at high speed and with minimal noise, using a comparatively inexpensive printing apparatus, and are rapidly becoming widespread.
In terms of the inks for these systems, aqueous inks are becoming more prevalent, as they are capable of producing high-quality printed items at low cost. Aqueous inks are inks in which water has been included to enhance the drying properties, and compared with oil-based inks, offer the advantages of resistance to show-through (penetration of the ink through to the underside of the recording medium) even if double-sided printing is conducted onto plain paper, and favorable text reproduction. The colorants used for these aqueous inks can be broadly classified into dyes and pigments, and of these, pigment inks tend to be rapidly gaining in popularity, as they offer superior levels of light resistance and water resistance.
Examples of problems that may occur when printing an aqueous ink onto plain paper include the phenomena of curling (convex curling) and cockling (wrinkling). These phenomena occur because the aqueous ink penetrates rapidly into the plain paper fibers of the recording medium, causing cleavage of the hydrogen bonds between fibers, and causing the paper to swell.
Patent reference 1 (Japanese Patent Laid-Open No.2005-220296) discloses an aqueous ink for an inkjet that comprises a solvent medium with a specified surface tension, viscosity and vapor pressure, and this ink exhibits improved discharge characteristics within the recording head, improved decapping properties, and excellent show-through resistance, text quality and curl properties.
Patent reference 2 (Japanese Patent Laid-Open No. H10-130550) discloses an ink that is suitable for color printing, the ink comprising water, a dye, a polyhydric alcohol lower alkyl ether, a nonionic acetylene glycol, and glycerol or a specific polyhydric alcohol, and this ink exhibits excellent curling prevention capabilities.